Experimental Analysis of Pressure Pulsation Noise Phenomenon in a CNG-Powered Passenger Vehicle

Compressed Natural Gas (CNG) engine has proved itself to be a worthy replacement for conventional fuels like gasoline & diesel in heavy commercial and passenger transport applications all over the world. Natural gas can be used to reduce carbon dioxide emissions while the global distribution of natural gas allows energy independence for regions with gas rather than oil reserves. In India, infrastructure development of CNG distribution and stringent emission regulations have increased the interest shown by Original Equipment Manufacturers (OEM) to concentrate towards development of CNG vehicles in every segment. From noise & vibration perspective, CNG powered vehicles are expected to maintain the same level of cabin refinement as their fossil fuel equivalents. However, one of the major challenges associated with CNG vehicles is the excitation due to additional components like CNG Pressure Regulator, Injector et al. The operational metallic / pulsation noises are generally higher as compared to liquid fuels like gasoline due to dry nature of the CNG fuel. This paper describes in detail the pulsation noise phenomena encountered during one of the late-stage vehicle development projects. An experimental root cause analysis methodology was established to identify the structural & cavity resonances phenomena of the CNG Regulator & Low-Pressure gas column along with identification of frequencies of various CNG sub-systems. Studies were carried out to de-couple resonance behavior of the system and improve attachment point stiffness as potential improvement solutions to mitigate this noise. The study also helped to define design guidelines to avoid such issues in future similar development models.